Prof. Ashwini Nangia from the School of Chemistry and PhD student Mr Rajesh Goud at the University of Hyderabad have proved that eye infection treatments that resist being blinked away could be formulated by cocrystallising an antibiotic with caffeine.
Prof. Ashwini Nangia
Prof. Ashwini Nangia of the School of Chemistry and PhD student Mr Rajesh Goud at the University of Hyderabad (UoH) have researched and proved that eye infection treatments that resist being blinked away could be formulated by cocrystallising an antibiotic with caffeine.
Cocrystallising sulfacetamide (left) with caffeine (right) makes it less soluble
Sulfacetamide (SACT) is often lost on blinking and in tears when applied as a treatment for conjunctivitis and other ocular ailments. This leads to the inconvenience and complications of applying larger and more frequent doses of SACT. Various schemes have been investigated, including trapping SACT in bioadhesive microspheres, to slow drug release and prevent its washout. But these either limited the drug’s bioavailability or weren’t suitable to market.
To solve the problem, Prof. Nangia and his colleagues at UoH, looked to cocrystals. Crystallising an existing drug with another safe substance can change the physicochemical properties of a medicine without having to change the drug molecule itself. The team reasoned that replacing weaker hydrogen bonds in the crystals with stronger ones could lower the crystal’s solubility and dissolution rate. A selection of molecules were therefore cocrystallised with SACT. The identification of intermolecular interactions which can be altered by cocrystal formation is what makes this research noteworthy and stand out among such design strategies.
Sulfacetamide and caffeine molecules pack together tighter than sulfacetamide alone
Caffeine proved to be one of the most successful, making the drug less soluble and the crystals denser – suggesting the molecules packed tighter together – compared to SACT alone. After studying the hydrogen bonding in SACT and in the cocrystal, stronger N–H—O bonds in the latter (compared to C–H—O) were found to cause the denser crystal packing and lower solubility.
The above has been published in the International Journal – Chemistry World and can be accessed at
http://www.rsc.org/chemistryworld/2014/03/caffeine-sulfacetamide-conjunctivitis-solubility-washout